This invention relates to an X-ray sensitive amplifier tube, and more particularly to an X-ray sensitive amplifier tube for use as an array detector in computerized tomography.
In some types of X-ray computerized tomographic systems a fan-shaped X-ray beam source is moved in a predetermined pattern over a patient and a moveable or stationary X-ray detector on the opposite side of the patient detects the X-ray image which is thereby produced. The X-ray detector is actually an array of X-ray detectors for detecting the fan-shaped beam at discrete intervals. The cost of manufacturing this array of detectors is quite large in a conventional system. It is also difficult to align the detectors properly and they often have dissimilar gain characteristics, making operational adjustments to the system difficult. Still another disadvantage of some prior art systems is that the thickness of the scintillation screens in the X-ray detectors are limited by spacial resolution requirements. This can limit the sensitivity of the system or else require a higher X-ray dosage which is undesirable for the patient. Still a further problem of the X-ray detectors in such systems is that because of the low light level produced at the output screen additional relatively expensive, high gain light detectors are required.
A suitable X-ray amplifier-detector tube which overcomes many of the manufacturing cost and alignment problems is an X-ray amplifier tube of the proximity type design, such as that disclosed in the applicant's previous application, Ser. No. 741,430, referred to above. Such a tube of the type disclosed in that patent application is not quite as suitable without modification, however, as an array detector. Before such a tube can be used as an array detector it must be segmented to produce an array of amplifying elements which have minimum influence upon or cross-talk with other members of the array. This is extremely essential in applications for computerized tomography since each detector in the array must have maximum independence to give a subsequent image reconstruction with minimum corrections and a high resolution.
There are four main sources of cross-talk in a proximity type, X-ray image array, intensifier tube:
(a) cross-talk due to light spreading in the scintillator screen, PA1 (b) cross-talk due to light from the scintillation screen which passes through the photocathode and is reflected back to it by the output screen, PA1 (c) cross-talk due to reflections of (or back scattering of) photoelectrons by the output screen, and PA1 (d) cross-talk due to light spreading in the output screen. PA1 (e) cross-talk due to the feedback of X-ray bremsstrahlung and ions produced at the output screen by the bombarding of photo-electrons.